The present invention relates to hydraulic fluid supply systems and more particularly relates to such of those systems which have return fluid filter assemblies located within fluid supply reservoirs.
Fluid supply systems of a type to which the present invention pertains are normally constructed to have unfiltered return fluid enter the bottom of a filter element mounted in the reservoir. In some of these systems, as represented by U.S. Pat. No. 3,847,243 issued to Barth on Nov. 12, 1974, the reservoir includes a return fluid compartment located below the filter assembly and return fluid plumbing is connected to the compartment which is in turn connected in fluid communication with the bottom of a filter element. In others of these systems, as represented by U.S. Pat. No. 3,960,174 granted to Latimer et al on June 1, 1976, the return fluid plumbing is connected directly in communication with the lower end of the filter element.
A common drawback exists in the two ways disclosed in the aforementioned patents for conveying return fluid into the filter element. Specifically, in both cases unfiltered fluid will drain from the filter element as the latter is being withdrawn from the reservoir for replacement. The patented Barth design has the further drawback that in the event of a failure in the return fluid plumbing or in components connected thereto, a considerable amount of fluid might drain from the reservoir due to the failure or might have to be drained from the reservoir before the failed component can be replaced.
It is here noted that the patented Latimer et al design does not suffer the last-mentioned drawback as the return fluid inlet thereof is located in the filter at a level above that to which the reservoir containing the filter assembly is intended to be filled. However, the Latimer et al design is not entirely satisfactory since it requires a considerable amount of space in the top of the reservoir to be kept empty and space is always at a premium on vehicles.